Five people died after a tour helicopter carrying six people crashed into the East River Sunday evening, FDNY and NYPD officials said.

Though helicopter crashes in the East and Hudson Rivers are not necessarily uncommon, this becomes one of the deadliest in the city's history, and one of the worst civilian aviation fatalities of any kind in the United States over the last few years.

The five passengers became trapped in the overturned helicopter and had to be pulled from frigid waters by divers, officials said. Three of them were taken to area hospitals in critical condition, while the other two were pronounced dead at the scene.

FDNY spokesman Jim Long said shortly before 1 a.m. Monday that the three critically injured passengers had died; two of them were at Bellevue Hospital and a third was at NYU Medical Center.

The pilot of the helicopter, who managed to escape, was the only survivor. Law enforcement sources identified him as Richard Vance, 33, and said he was released at some point overnight.

Separately, sources indicated the dead were four men and one woman, though identities were not immediately available.

At a press conference Sunday night, FDNY Commissioner Daniel Nigro said the pilot was able to free himself and was taken by a fire boat to shore. Nigro described the pilot as being OK. He said he was taken to Cornell Medical Center, where he remained early Monday.

"It's a great tragedy that we had occur here on an otherwise quiet Sunday evening," Nigro said.

The helicopter went down in the waters near East 86th Street and the FDR Drive shortly after 7 p.m., according to officials, who said police received dozens of 911 calls in the minutes after the crash.

"Mayday... Mayday... Mayday... East River engine failure!" the pilot said during a distress call moments before losing control of the helicopter and plummeting into the water.

Witnesses said the pilot was waving with both arms and yelling "Help!" from the water.

Officials said the helicopter, owned by Liberty Helicopter Tours, was a private charter out for a photo shoot.

Chopper 4 reporter Kai Simonsen says passengers on such flights are usually strapped in as they take photos of the city. The passengers are normally shown a safety video before going up that instructs them to use a cutter on their harness to break free during an emergency, Simonsen says.

But after FDNY and NYPD harbor and aviation units descended on the crash site, divers discovered the five passengers still strapped into their harnesses inside the submerged helicopter. Nigro said the East River had currents of 5 mph and waters below 40 degrees at the time.

"The five people besides the pilot were all tightly harnessed, so these harnesses had to be cut and removed in order to get these folks off this helicopter, which was upside down at the time and completely submerged," Nigro said.

The Coast Guard and a private tugboat also assisted in the rescue, according to NYPD Commissioner James O'Neill, who said the tugboat crew were the first to arrive after the crash.

Videos on social media show the red helicopter crashing into the water around sunset. The chopper's propellers swing wildly in the water before the aircraft overturns and sinks.

Other videos show emergency responders rushing to the water as crowds of onlookers gather at the shore.

The helicopter was recovered and towed to 23rd Street and the FDR Drive, where it was still submerged around midnight.

The crash happened right in front of Gracie Mansion, the official residence of Mayor Bill de Blasio, who was out of town this weekend.

In a statement earlier in the evening, Gov. Andrew Cuomo said he was monitoring the situation.

"Our thoughts and hope for safe recovery are with those who were aboard. We are thankful for our first responders at the scene," Cuomo said.

The FAA said confirmed in a statement that a Eurocopter AS350 went down in the East River near the northern end of Roosevelt Island. The agency said the National Transportation Safety Board will lead the investigation in determining what caused the crash.

The Aviation Safety Network, which tracks flight accidents and fatalities, had recorded at least 11 other fatal crashes worldwide involving AS350 variants over the last 18 months alone.

According to that same database, Sunday's crash is likely the biggest U.S. civil aviation fatality since a December 2016 Cessna crash in Ohio.